A physician had acquired the habit of using and misusing cocaine for the treatment of a disease of his nose. The habit grew to a craving for cocaine while the cocaine itself poisoned the brain. Acoustical hallucinations began; he heard voices from every corner of the room, and on the street the voices took persecutory character. He connected them with his brother living in Europe, heard his voice in the denunciations, and developed a pathological system of ideas around the central thought that his brother had a telepathic influence on him. His reason succumbed, he lost all consciousness of delusion, and believed himself really to be under the control of the absent brother. When he came to me he had been without sleep and without food for several days, and he was not seeking my help to get rid of the mental disturbance but to overcome the power of his older brother. He did not connect the fear at all with his misuse of cocaine. When I discovered the role which the cocaine played, I determined to try the suggestive influence, the more as I found that he was in a half-hypnotic state as soon as he had entered my room. I suggested to him to sleep and to take food and to reduce the cocaine dose by a fourth. The next day he was an entirely different man by the effect of ten hours' sleep and a large breakfast. Now I concentrated my efforts on the reduction of the cocaine. After ten days of hypnotic treatment he gave up cocaine entirely, after three weeks the voices disappeared and slowly the other symptoms faded away. The pathological idea of the telepathic influence lasted a while after the voices had gone until this idea, too, yielded to suggestion. It still took six weeks before he himself felt that he was entirely normal.